Patent GB-793238-A (GB)
Title: Improvements in or relating to indicators for aircraft drift, ground speed and distance run
Inventor: MORGAN MERVYN
IPC: G01S13/60
Filed: 1953-11-06
Abstract: 793,238. Electric indicating systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 8, 1954 [Nov. 6, 1953], No. 30845/53. Class 40 (1). [Also in Group XL (c)] A Doppler effect aircraft drift and/or ground speed and/or distance run indicator comprises a set of resonators resonant to different closely spaced frequencies within and covering the expected band of Doppler frequencies, means for feeding to the resonators the Dopplerfrequencies from two parts of the aerial system in turn, means for successively sampling the outputs from the resonators of the set during each period when an aerial part is operative, means for producing, simultaneously with the taking of each sample, a different predetermined D.C. voltage allotted to and characteristic of the resonator being sampled, means responsive to an output of a predetermined minimum value from any resonator of the set for supplying the predetermined D.C. voltage simultaneously produced to one or other of two voltage storage circuits, one of which is connected to receive the D.C. voltage in alternate periods, and the other of which is connected to receive the D.C. voltage during the remaining periods, and means responsive to the stored voltages in the storage circuit for orientating the aerial system and/or for varying the frequency of a reference frequency source the frequency of which is a function of aircraft speed. The system may comprise two pairs of aerials AB, CD, Fig. 2, directed to the port bow and starboard quarter and to the starboard bow and port quarter; the outputs from the aerials are fed alternately by means of a switch 1 to a receiver demodulator and an amplifier 4 which feeds a sensitive frequency discriminator 8; this controls the frequency of a phonic wheel generator 10 through a saturable reactor 17, and also, through a switch 6 operated synchronously with switch 1, controls two saturable reactors 23, 24 which in turn control the aerial motor 31 so that the aerial is aligned to the " on track " position. The frequency of the generator 10 is a measure of aircraft speed and can be used to operate a speed indicator and/or a counter calibrated in miles run. If the aerials are too much off track or the frequency of generator 10 is too far from the correct frequency, the discriminator 8 will be unable to take charge, and therefore according to the invention the output of amplifier 4 is also fed to a number of resonant circuits 36 tuned to adjacent different frequencies spaced in the Doppler spectrum to be expected. Each resonant circuit is provided with a rectifier and is connected to a separate contact on a distributer switch 40 which is driven synchronously with another distributer switch 41, the contacts of which are connected to different points on a potentiometer 43 so that whenever the brush of switch 40 is on a contact the brush of switch 41 is on a corresponding contact and therefore receives a predetermined D.C. voltage allocated to, and characteristic of, the frequency of the resonator connected to the brush of switch 40. The brush of switch 40 is connected to the grid of a valve 47 which is normally cut off, but if the brush is on a contact connected to a resonator whose frequency is substantially the same as an incoming Doppler frequency from amplifier 4, the resonator will supply a sufficient positive voltage to render valve 47 conductive. When the valve 47 conducts a trigger circuit comprising valves 50 and 51 is trigger and causes valve 52 to conduct; this allows condenser 66 or 67, according to the position of switch 7, to be charged to a potential corresponding to that on the brush of switch 41. Switch 7 is driven synchronously with switches 1 and 6, and the potentials on condensers 66, 67, which correspond to the Doppler frequencies, are fed through valves 68, 69 to saturable reactors 23, 24 to correct the aerial alignment and to saturable reactor 17 to correct the frequency of the phonic wheel generator.